1. Field of the Invention
The present invention relates to a process for controlling the extraction rating of a gas extractor for an enclosure of a cryogenic apparatus furnished with a cryogenic fluid feed, said apparatus being in contact with the ambient medium.
The invention furthermore relates to a cryogenic apparatus implementing such a control process.
2. Description of Related Art
The invention is concerned in particular with deep-freezing tunnels comprising liquid nitrogen feed means and means for extracting the vaporized nitrogen which are formed by a chimney fitted with an extraction fan.
Such a tunnel comprises openings for loading and extracting articles for freezing and which have been frozen. Gaseous exchanges between the ambient medium and the atmosphere prevailing in the enclosure of the tunnel take place through these openings.
In the case in which the extraction flow rate is too high, hot and moist air enters the enclosure of the tunnel. Numerous drawbacks arise from this. In particular, as a result of the air being at a temperature greater than the temperature prevailing in the enclosure, there is excessive consumption of cryogenic fluid so as to maintain the temperature in the enclosure constant. Moreover, in the air being laden with moisture, there is formation of ice and frost on cooling the air both in the enclosure of the tunnel and also in the extraction chimney.
Conversely, if the extraction flow rate is too low, the cryogenic fluid is not completely discharged via the chimney and spills out of the enclosure of the tunnel, thus modifying the composition of the ambient medium. Thus, current cryogenic tunnels cannot be used in enclosed spaces on account of the risks of creating an under-oxygenated atmosphere of danger to staff.
Currently, the extraction rate is adjusted manually. In practice, the individual in charge of this adjustment assesses visually the direction of the gas flow set up between the enclosure of the tunnel and the ambient medium. They attempt to zero this flow by altering the extraction flow rate. However, it is observed that, in practice, so as not to risk an under-oxygenated atmosphere, the adjustment is made in such a way that the ambient air enters the interior of the cryogenic tunnel continuously. The problems set forth above then adversely affect the proper operation of the apparatus.